Confused 😩

Hey just wondering if anyone has ever had a 2 day period then brown spotting afterwards, the day before I done a test and had a faint line on a FR, then came on the 2 day "period" no clots .. After it finished I done another test the other day came up with a very faint line, then done one the next day and said negative which was clear blue ..
I was on anti biotics a few weeks ago, can it be that messing with my period? 
Now I have mild back and stomach systems like I'm going to come on my period and I'm constipated ... I'm sooo confused.. Is this a chemical pregnancy?